In a continuation of our study into the structure and function of the opiate receptor system, the first enantiomeric pair of alkylating opiates have been prepared. These enantiomers have been shown to exhibit substantial stereo-selectivity for the delta opiate from NG108-15 cells. A mu selective ligand based on etonitazene has been tritiateded to high specific activity. Other alkylating opioids have been prepared and characterized biochemically.